Hi, new here. I've searched around here before but decided to finally post today. I've been building up a modular type synth of mostly cheap simple little circuits, 555 lfo timers, 4017 sequencers, Atari punk consoles, stuff like that. It is coming along pretty good but I've been finding that if I try to run them all off the same power supply (a wall wart run in parallel) they seem to have weird ground issue's? For instance, if I have a sequencer multed out to two apc they wont work right. Ive also noticed if I turn one of there powers on while they are hooked up they both turn on. I've found that pretty much all of these circuits do weird things if I run them off the same power supply where as if I run them off batteries they work fine. I've tried various different things with diodes and also some transformers I have laying around but nothing seems to effect it? Im assuming I need to isolate one circuit from another but I can't seem to figure out how? Any ideas?

Ive also noticed if I turn one of there powers on while they are hooked up they both turn on.

What ? Your… your machine is… alive !!!

More seriously, hello and welcome. These are weird symptoms indeed ! Could you elaborate about your switching device ? It's a bit scary ! (in case the switch is the classical «stompbox jack in» type, and another jack is inserted in said module, it just normal, the jack's shield/ground makes connection)
For the rest, how good are the PSUs you tried ? Are they regulated ? Are they powerful enough ? Did you measure the current draw of your modular ? From what you describe, your synth is likely not that greedy, though. Can you try to run, say your seq + 2 APCs from one battery and see how they behave ? Can you run your setup on batteries and switch modules one after the other to the Wallwart PSU (with great care of course) to try to determine if there's a faulty module / combination / whatever intriguing fact ? And what makes you think it's a ground issue ? (for what it's worth, your ground wires and tracks should the thick and broad, without «weak points» along the way nor redundant connections)
Sorry if you already tried/checked all this, I don't have your synth in front of me, so I'm just guessing…
Besides, I wouldn't mind to see or hear more of your cheaposynth !_________________::U::N::S::C::H::N::E::L::L::

thanks for the reply. I will try some of those suggestions after I get off work later. I will also post some pictures of the front and the back. The switch's are just spst toggle switches, each module has its own. I haven't checked the current draw but I can't imagine these circuits use much at all. The two apc's are synthrotek.com kits. I have two different sequencers and the mults I just wired up myself. I will try using one battery to run all of them and see how that works. I guess I don't have much reason to think its a grounding issue except I do?

OK, a little more testing leads me to think it might be easier if people could throw out some ideas as to how they are powering multiple circuits like this? Its so funky how things dont want to work together?

yes, i have encountered the same problem, as my live setup uses 8 keyboards and boss effect pedals, connected to a 8 track mixer.

i used a 1700m ampere 9v adapter. when i hook up some of my instruments it is fine. but some combinations gives a hiss that resembles the sound of a howling dog (high frequency).

some keyboards seem not to be able to run parallel without increasing the hiss. especially yamaha (PSS series, 100, 570). sometimes these even lose power while connecting the other keyboard.

as far as i experienced, the problem starts with connecting jacks to the output channel. a friend of mine who is more a technician than i am, says it is indeed a ground problem because the jacks connect the ground to the mixer and there is "too little ground" to connect more keyboards. hope i express it right, i am not an expert in electricity circuits... just some ideas

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